Method and apparatus for continuous monitoring of fluoride effluent



Aug. 12, 19,69 G. o. GUERRANT 3,461,043

.METHOD AND APPARATUS FOR CONTINUOUS MONITORING OF FLUORIDE EFFLUENTFiled May 5, 1965 Q in i.; s M 22 :lf "15 2| #i l? 2 a 4 r.

INVENTOR.' GORDON O. GUERRANT United States Patent O 3,461,043 METHODAND APPARATUS FOR CONTINUOUS MONITORING F FLUORIDE EFFLUENT Gordon O.Guerraut, Stone Mountain, Ga., assignor, 'by

mesne assignments, to USS Agri-Chemicals, Inc., Pittsburgh, Pa., acorporation of Delaware Filed May 3, 1965, Ser. No. 452,610 Int. Cl.B011; 3/00 U.S. Cl. 204--1 7 Claims ABSTRACT 0F THE DISCLOSUREContinuous monitoring of uoride eluent by internal electrolysis isaccomplished by contacting fluoride containing gas in tubing with anacid electrolyte and the electrolyte then passed through an electrolysiscell having electrodes for spontaneously generating current ow, theelectrolyte being introduced by a capillary to form a lm on the tubingwalls and in Which the lluoride is absorbed, the gas being removed andthe electrolyte free of gas being passed through the cell and withdrawn,the current flow being measured.

This invention relates to the continuous monitoring of uoride etiluentby internal electrolysis, and more particularly to a process andapparatus for the continuous monitoring of fluoride evolution from aphosphatic fertilizer manufacturing operation or like operation in whichgases containing volatile tluorides are produced or discharged into theatmosphere.

A primary object of the invention is to provide a continuous uoridemonitor for the purposes set forth above, Another object is to provide asimple continuous uoride monitor with remote recording for use in eluentpollution control of phosphate plant emission. A further object is toprovide a iluoride monitor device of simple and compact structure whichmay be utilized in the eld and in operating plants for the effectivedetermination and control of iluorides in waste gases, etc. Otherspecific objects and advantages will appear as the specificationproceeds.

The invention is illustrated by a specific embodiment and may beemployed in connection with apparatus shown in the accompanying drawingin which FIG. 1 sets out a diagrammatic showing of the apparatus andFIG. 2 is an enlarged vertical sectional view of an electrolysis cellwhich may be employed.

In the illustration given, an electrolyte material from a reservoir 9o'ws by gravity into the tubing 10. The tubing 10 communicates with aT-fitting -11 having a gas inlet projection 12 communicating with a gasinlet tube 13. A capillary in the form of a hypodermic tubing 14 extendsthrough a neoprene seal 15 in the lower portion of tubing 10 anddownwardly into the lower portion 16 of the T-tting and into the mouthof a small diameter tube 17. The tube 17 extends through a seal 18 inthe lower fitting portion 16 and upwardly as above described to a pointwhere it receives the outlet end of the hypodermic tubing 14. By thismeans, electrolyte is fed into the small diameter tube 17 where it isspread out in a thin lm on the walls of the tube for intimate contactwith the gas which is introduced through pipe 13.

By delivery of the electrolyte directly into the capillary, minimumelectrolyte volume is required for absorption of gaseous iluorides toprovide maximum response. Also the gas velocity in this scrubber tube 17increases the flow by producing some aspirating action on theelectrolyte ilow through the needle.

The proportions of the various parts described above may be variedsubstantially. However, for the purpose of illustration, the capillarymay be one inch of No. 25

3,461,043 Patented Aug. 12, 1969 ICC gauge hypodermic tubing and issuilicient for providing one liter per day ow so that from a live-gallonreservvoir the feed rate is suiiicient for two Weeks of operation.Further, by way of example, the tube 17 to which the needle deliverselectrolyte may have a diameter of 0.125" O.D. and an inside diameter ofapproximately 0.079", which provides good results with a pressure dropof 40 mm. (75") of mercury at an airilow of 1.5 l./min.

The tube 17 delivers the gas and electrolyte into a treating vessel 19which may be of any suitable shape or construction. I prefer to employ atreating vessel in the shape of a vertically elongated loop, as shown inthe drawing and which comprises a larger tube, as, for example, a tubeof 0.375 outside diameter. The tube 17 empties into the upper portion 20of a treating leg having in the lower portion of the leg an electrolysiscell, designated generally by the number 21. The electrolysis cell isprovided with aluminum and platinum electrodes preferably embedded in aplastic, such as polyethylene, etc., tube 22, the aluminum electrode 23and the platinum electrode 24 being spirally arranged and held by theplastic tube within the enlarged tube 19a. The electrodes communicateIwith a terminal block 25 from which cables lead to a recorder which maybe located at a substantial distance from the treating vessel 19. Sincesuch instruments for measuring the current flow and for recording thesame are 'well known, a further detailed description herein is believedunnecessary.

The opposite leg of the treating vessel 19, namely, vertical leg 26, isprovided at a point above the center thereof with a T-titting 27 havingan outlet connection 28 communicating with the outlet tube 29. Theoutlet tube 29 preferably passes into a receiver 31 through a flow meter30 and from thence to vacuum. Communicating with the sealed receiverthrough the pipe 32 is a pump device for maintaining a reduced pressureor vacuum upon receiver 31, as, for example, a dry vane-type airsampling pump.

The electrolyte may be any suitable acid material, such as, for example,dilute acetic acid, and to such acid I prefer to add a wetting agent anda small amount of fluoride. For example, the electrolyte may consist of6% acetic acid, 0.01% wetting agent, and 0.05 mg./l. ot' fluoride. Byway of example, the reagent may consist of 60 ml./l. of acetic acid, 0.1ml./l. of Tergitol non-ionic NPX, and 0.5 ml. of 0.01% HF per liter. Thewater used should be copper-free, either deionized or distilled, and notcontacted with copper or brass lines after purication.

OPERATION In the operation of the process and apparatus, I prefer tomaintain a liquid head in the tubing 10 of approximately 12, owtherefrom being regulated by the capillary 14. The electrolyte deliveredby the capillary 14 into the small diameter tube 17 is spread out in athin film on the walls of the tube for intimate contact with the gasand, during the passage through tube 17 before reaching the treatingvessel 19, the fluoride content is absorbed in the electrolyte. The gasand electrolyte from the scrubber tube 17 are delivered into the leg 20of the treating vessel 19 at a substantial distance (preferably about 4)above the electrodes of cell 21. The electrolyte falls into the cell,while the gas (air) separates and ows over the top leg 33 and downwardlyinto the outlet leg 26, being withdrawn through the outlet tube 29 tothe vacuum receiver 31. Thus, the gas by-passes the cell 21 and isvented through the pump (not shown) communicating with the vacuum tube32. The electrolyte ows through the spirals of the cell by gravitydownwardly through leg 20 and thence upwardly through leg 26 to theoutlet tube 29. The liquid level in the cell is determined by thelocation of the T-fitting 27, and the location is such that all of theelectrode spiral is below the cell liquid level. The vertical section ofthe leg above the cell is important in that it permits liquid build-up,in the event of gas blockage, so as to restore normal operation. Thisvertical area in the upper portion of the leg 20 prevents electrolytefrom bypassing the cell 21 in the case of gas blockage.

The bottom leg 34 of the treating vessel 19 is inclined upwardly towardthe leg 26, and the upper leg 33 has generally the same inclination. Thetop leg portion 33 is designed to drain into the electrode leg 20 andthe bottom leg portion 34 aids in causing gas bubbles to ow out afterentering this region.

Specic examples illustrative of the process and apparatus may be set outas follows:

EXAMPLE I An apparatus was set up, as shown in the figure, using a cellemploying a coil of aluminum wire embedded in an 0.25" O.D. x 3-4"polyethylene tube, the embedding being done by melting a spiral grooveinto the tubing with a pitch of approximately four grooves per inch. Aplatinum wire 24 was similarly arranged. The tubing was mounted withinthe vertical leg 20 of a treating vessel or tube 19a formed ofpolypropylene tubing. The recorder was a laboratory recorder. Thehypodermic tubing was from 1.25 long ZS-gauge hypodermic needle. In theassembly ofthe electrode spiral, an 0.31 I.D. tubing 19a was slippedover the electrode spiral for assembly.

The electrolyte consisted of 60 ml./l. of an acetic acid, 0.1 ml./l. ofTergitol non-ionic NPX, and 0.5 ml. of 0.01% HF per liter. Calibrationof the instrument for response to iiuoride may be accomplished byintroducing gaseous standards containing liuoride in air or byintroducing a metered micro amount of aqueous uoride or by comparison tothe integrated iiuoride concentration obtained by absorption of aparallel sample in an impinger. Anhydrous HF is the most convenient inCalibrating the instrument for use.

In the test operation, calibration was accomplished by means of astandard prepared by metering air into a polyethylene drum liner andadding the 10-30 ml. of anhydrous HF with a polyethylene syringe.Maximum instrument response is checked by direct introduction ofanhydrous HF, with approximately one hour required for completerestoration to base line operation.

Electrolyte was delivered at the rate of 0.3 gallon per 24 hours, withthe response for initial time being 0.5 minute and for 90% signal time 5minutes and for recorder deiiection mv. 60. The recorder was located 250feet from the laboratory, and the instrument showed an immediateresponse to the uoride content in the gas being treated.

EXAMPLE II The process was carried out as described in Example I in aFlorida plant operating for the manufacture of triple superphosphate andin connection with a dryer stack. The warm gases from the stack Werewithdrawn and passed through the apparatus and with an immediate recordresponse showing the varying content of the fluoride in the gases beingprocessed.

While in the foregoing specification I have shown specific embodimentsof the invention in considerable detail for the purpose of illustratingthe invention, it will be understood that such details may be variedWidely by those skilled in the art without departing from the spirit ofmy invention.

I claim:

1. In a process for continuous monitoring of uoride effluent by internalelectrolysis in which fluoride-containing gas is contacted in a tubingwith an acid electrolyte and absorbed by the electrolyte and theelectrolyte then passed through an electrolysis cell provided withelectrodes for spontaneously generating current iiow, the steps ofintroducing the electrolyte by a capillary to form a lm on the tubingwalls, introducing gas containing uoride and contacting the electrolytetherewith for absorption of the fluoride, removing the gas, and passingthe electrolyte free of the gas through said cell, measuring the currentflow,

5 and continuously withdrawing electrolyte from said cell.

Y 2. tThe process of claim 1 in which a vacuum is maintained incommunication with the electrolyte entering the cell and the electrolyteleaving said cell.

3. In a process for continuous monitoring of fluoride eliuent byinternal electrolysis in which fluoride-containing gas is contacted in atubing with a dilute acid electrolyte and absorbed by the electrolyteand the electrolyte then passed through an electrolysis cell providedwith electrodes for spontaneously generating current flow, and currentow measured, the steps of introducing the electrolyte by gravity andunder a liquid head through a hypodermic needle into the tubing to forma lilm on the walls thereof, introducing gas containing fluoride intothe tube for contact with the electrolyte-coated walls for absorption bythe electrolyte of the fluoride, removing the gas, passing theelectrolyte substantially free of the gas through said cell, andcontinuously withdrawing said electrolyte from said cell.

4. In apparatus for continuous monitoring of fluoride eluent by internalelectrolysis, an absorption tube of small diameter, capillary means forintroducing a dilute acid electrolyte in a thin lm onto the inner wallsof said tube, means for introducing gas containing iiuoride into saidtube for absorption by the electrolyte, a treating vessel generally inthe shape of a vertically elongated loop, electrodes in the lowerportion of one leg of said vessel forming a cell for spontaneouslygenerating current, means for measuring said current, said tube beingattached to said vessel so that its outlet communicates with the upperpor- 35 tion of said vessel above said cell, an outlet tubecommunicating with the other leg of said vessel at a point aligned witha point on said rst leg above said cell, a receiver Vessel communicatingwith said outlet tube, and means for maintaining said receiver and saidtube under vacuum.

5. The apparatus of claim 4 in which the two vertical legs of theapparatus are connected by inclined legs of generally parallelinclination.

6. The apparatus of claim 4 in which a T-itting eX- tends between theinlet to the capillary and the absorption tube and is providedtherebetween with an inlet for receiving gas.

7. In a process for continuous monitoring of fluoride eiliuent byinternal electrolysis in which uoride-containing gas is contacted in atubing with a dilute acid electrolyte and absorbed by the electrolyteand the electrolyte then passed through an electrolysis cell providedwith electrodes for spontaneously generating current ow, and currentiiow measured, the steps of maintaining the aqueous component of thedilute acid electrolyte substantially free of copper, introducing theelectrolyte into the tubing to form a lm on the walls thereof,introducing gas containing uoride into the tubing for absorption by theelectrolyte of the iiuoride, removing the gas, and passing the G0electrolyte substantially free of the gas through said cell.

References Cited UNITED STATES PATENTS 2,864,747 12/1958 ROth 204-1952,884,366 4/ 1959 Anderson et al 204-195 3,050,371 8/1962 DOWSOII et al204--195 3,058,901 10/1962 Farrah 204-195 3,131,133 4/1964 Barendrecht204-237 JOHN H. MACK, Primary Examiner T. TUNG, Assistant Examiner U.S.Cl. X.R.

